Is Elective Inguinal or External Iliac Irradiation During Neoadjuvant (Chemo)radiotherapy Necessary for Locally A dvanced Lower Rectal Cancer With Anal Sphincter Invasion?

PURPOSE: To investigate the impact of excluding irradiation of inguinal lymph nodes (ILNs) and external iliac lymph nodes (ELNs) during neoadjuvant (chemo)radiotherapy in a locally advanced lower rectal cancer (LALRC) with anal sphincter invasion.

METHODS AND MATERIALS: A total of 214 LALRC patients with anal sphincter invasion according to pre-treatment magnetic resonance imaging who underwent neoadjuvant (chemo)radiotherapy followed by surgery between September 2010 and May 2019 were enrolled. ILNs and ELNs were clinically negative pre-treatment and were excluded from irradiation. Failure rates and patterns of ILNs and ELNs and survival were analyzed. Nomograms for predicting ILN and ELN failure risk were also constructed.

RESULTS

The median follow-up was 53.3 months. The 3-year failure rates were 3.7% for ILNs and 3.3% for ELNs. Only 1 patient developed isolated ILN failure, and no patient experienced isolated ELN failure. Multivariate analyses demonstrated that lower edge of tumors invaded or located below the dentate line (odds ratio [OR], 7.513; P = .013), high histological grade (OR, 6.892; P = .017), and perineural invasion (OR, 7.111; P = .023) were significantly related to ILN failure. Both perineural invasion (OR, 8.923; P = .011) and high histological grade (OR, 8.129; P = .011) showed a strong correlation with ELN failure. The concordance index of nomograms for predicting ILN and ELN failure risk were 0.842 and 0.880, respectively. The 3-year local recurrence free survival, disease-free survival, and overall survival were 94.6% (95% confidence interval [CI], 91.3%-97.9%), 77.7% (95% CI, 71.8%-83.6%), and 91.9% (95% CI, 87.8%-96.0%), respectively, for the whole cohort.

CONCLUSIONS

Excluding ILNs and ELNs from irradiation was associated with an acceptably low failure risk for LALRC invading the anal sphincter. These findings help to refine existing guidelines for clinical target volume delineation of ILNs and ELNs during neoadjuvant (chemo)radiotherapy in rectal cancer.